Conventionally, in order to improve the wear resistance, sliding characteristic, and protection function of a machine part, a cutting tool, a sliding part, etc., there has been widely used a physical vapor deposition method of coating a surface of a substrate, which is the part or tool, with a thin film. An arc ion plating method and a sputtering method are widely known as examples of the physical vapor deposition method. The arc ion plating method is a technology using a cathode-discharge arc evaporation source.
In the cathode-discharge arc evaporation source (hereinafter, referred to as arc evaporation source), arc discharge is generated on a surface of a target being a cathode, and hence a substance forming the target is instantly molten, evaporated, and ionized. The arc evaporation source attracts the substance ionized by the arc discharge to the substrate side serving as a subject to be processed, and forms a thin film on the surface of the substrate. In the arc evaporation source, since the evaporation speed of the target is high and the ionization rate of the evaporated substance is high, a dense coating can be formed by applying a bias to the substrate during the film formation. Hence, the arc evaporation source is industrially used in order to form a wear-resistant coating on the surface of the cutting tool or the like.
Target atoms, which are evaporated by the arc discharge, are highly ionized in arc plasma. In this case, transportation of ions from the target toward the substrate is affected by the magnetic field between the target and the substrate, and the path of ions extends along magnetic force lines extending from the target toward the substrate.
However, in arc discharge generated between a cathode (target) and an anode, when the target is evaporated around an electron discharge spot (arc spot) at the cathode side, the molten target (macroparticles), which is melted from an area near the arc spot and is before evaporated, may be discharged. The adhesion of the molten target to the subject to be processed may cause the surface roughness of the thin film to be decreased.
With regard to this, if the arc spot moves at high speed, the amount of macroparticles tends to be reduced. However, the moving speed of the arc spot is affected by the magnetic field applied to the surface of the target.
To address such a problem, a technology of applying the magnetic field to the surface of the target and controlling the movement of the arc spot has been suggested as follows.
PTL 1 discloses an arc evaporation source including an outer peripheral magnet surrounding the outer periphery of a target and having a magnetization direction along a direction perpendicular to a surface of the target, and a back side magnet having a polarity in the same direction as that of the outer peripheral magnet and having a magnetization direction in a direction perpendicular to the surface of the target. With this arc evaporation source, it is expected that the straightness of magnetic force lines can be improved.
PTL 2 discloses an arc evaporation apparatus that forms a parallel magnetic field on a surface of a target by a ring-shaped magnet arranged around the target and an electro-magnetic coil at a back side. With this arc evaporation apparatus, it is expected that arc can be induced according to any track from the center of the target to an outer edge portion.